The function of individual neurons in visual pathways is investigated by use of new techniques and instrumentation developed in this laboratory. The method, called Alopex employs response feedback and a set of algorithms which modify an initially random stimulus pattern. It has been shown that convergence on a receptive field is generally achieved in about 100 iterations. The method has the virtue of providing an automatic and unbiased approach to receptive field studies. The method is applied to frog retinal ganglion cells and cells in visual tectum. In ancillary anatomical studies the structure of visual areas is investigated by use of a computer-aided digitized measuring system.